(a) Field of the Invention
The present invention relates generally to visual displays. More specifically, the present invention relates to an organic light emitting device and a manufacturing method thereof.
(b) Description of the Related Art
Demand for lighter or thinner monitors and TVs is currently increasing, and cathode ray tubes (CRTs) are being replaced by liquid crystal displays (LCDs). However, because the LCD is a passive display device, an additional back-light is needed as a light source. Additionally, LCD displays have additional challenges, such as relatively slow response time and narrow viewing angle.
Among the flat panel displays, organic light emitting devices (organic light emitting diode display, OLED display) have recently been the most promising as a display device for solving these problems. The organic light emitting device includes two electrodes and an organic light emitting layer interposed between the two electrodes. One of the two electrodes injects holes, and the other injects electrons, into the light emitting layer. The injected electrons and holes are combined to form excitons, and the excitons emit light as discharge energy. Because the organic light emitting device is a self-emissive display device, an additional light source is not necessary. The organic light emitting device thus has lower power consumption, as well as relatively high response speed, wide viewing angle, and high contrast ratio.
Typically, the organic light emitting device includes a plurality of pixels such as red pixels, blue pixels, and green pixels, and images of full colors may be displayed by selectively combining these pixels. Also, a white pixel may be further included in addition to the red pixel, the blue pixel, and the green pixel to improve the luminance. However, the various light emitting materials used in the organic light emitting device have different light emitting efficiencies. This presents a challenge when materials having excessively low light emitting efficiencies fail to accurately reproduce colors.
To improve the light emitting efficiency, a micro-cavity may be used. In a micro-cavity, light is repeatedly reflected between a reflection layer and a transflective layer that are separated by a predetermined distance (an optical path length), such that a strong interference effect is generated in the light. Accordingly, light of a specific wavelength reflects constructively, and light of remaining wavelengths reflects destructively. By tuning the micro-cavity to desired wavelengths, the luminance and the color reproducibility of the display may be simultaneously improved.
However, this approach tends to require micro-cavities for each pixel, increasing the number of fabrication processes, and thus increasing fabrication time. Also, the presence of micro-cavities in white pixels may alter a portion of the white spectrum.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.